Conveyor systems are widely used to move objects from a first location to a second location. Conveyors can take on a wide variety of characteristics, depending, in part, on the nature of the goods being moved, on the environmental conditions in which the conveyor will be used, and the specific path of the conveyor including changes in vertical elevation, turns and the radii of the turns.
One type of conveyor is a power roller conveyor. Power roller conveyors have a plurality of rollers drivingly connected with a driving means such as an electric motor. The rollers are engaged, directly or indirectly, by the goods being moved or conveyed. Rotation of the rollers moves the goods in a desired direction. Driving torque is communicated to each driving roller by a drive system commonly comprising in part a belt, a chain, or a drive shaft. Each type of drive system has certain advantages and disadvantages. Drive shafts are able to transmit high levels of torque to the rollers via gear sets connecting the drive shaft to the rollers, but such systems are expensive and can be difficult to service. Chain drive systems are durable and can also transmit high levels of torque to the rollers. Chains, however, require lubrication which may make them unsuited for use in clean environments. Belts typically do not require lubrication and are therefore cleaner than chains. Flat and V-belts, however, are somewhat subject to slipping. Known toothed belts have teeth on just one side and can only be drivingly engaged on that one side, making the possible relative orientations of the driving unit and the rollers more limited than those possible with chains.
The rollers in some conveyors are preferentially mounted in cantilever fashion to a supporting structural member. The rollers are typically rotatably disposed on a shaft which is fixed on one end relative to the structural member. The cantilever mounting arrangement facilities moving the rollers. However, the shaft must be sized sufficiently large to support a pallet or the like without bending.
Another concern with known conveyors is in preventing damage to both the conveyor and to the goods or objects being moved when the goods or objects being conveyed are stalled or jammed up on the conveyor. Such stalling can occur when goods accumulate at the end of the conveyor if there is a delay in removing the goods from the conveyor. The damage results from rollers continuing to rotate relative to the stationary goods. Also, such stalling may cause the motor to require more power to keep the rollers rotating at a constant speed. An oversized motor may be needed to ensure that the motor will not be stalled. One approach used to minimize the risk of damage and excess energy consumption is to provide a clutching mechanism between the roller and the drive gear. When a roller experiences drag torque exceeding a predetermined magnitude, as might occur with stalling of goods, the clutch slips, allowing the roller to stop rotating even though the drive belt and sprocket keep moving. For many clutching systems, the torque at which the clutch slippage occurs either cannot be adjusted at all or cannot be adjusted very easily.
Some known power roller conveyors rely on an axial deflection of springs, such as wave washers or Belleville springs, to generate a clutching preload. In some such power roller conveyors, there is relative rotation between the elements which axially contain the springs, either when the rollers are rotating or when they are stalled. This relative rotation can cause the springs to wear and deteriorate, decreasing the axial load the springs are able to provide and/or causing them to break. In one known clutching system in which the springs rotate in unison with the adjacent elements, the arrangement is not well suited for packaging into a cantilevered roller application.
Another concern with known power roller conveyors relates to the level of difficulty involved in both shifting the relative locations of the rollers to accommodate a change in package size and the ease of removal of the rollers from the conveyors. Many conveyors use bores in the supporting structure for mounting the rollers. This limits the locations of the rollers to the locations of the bores. Some supporting structures have longitudinally extending T-slots for fixing the rollers in place. The T-slots enable infinite adjustment of the space between the rollers. However, even with T-slots, the rollers are often more difficult to access and reposition within or remove from the conveyor's supporting structure by surrounding supporting members and guards.
A further concern with known belt or chain driven power conveyors employing separate left and right hand rollers relates to coupling the rollers to a common drive motor. Usually, a connecting shaft extends between the two sides. However, if the shaft is difficult to remove and/or install, then the chain or belt is consequently more difficult to remove and/or install.